Synergistic Effects of Biochar and Arabidopsis helleri on Soil Cd and Pb Bioavailability and Uptake and Disposition

The potential effects of combining biochar with hyperaccumulator plants on heavy metal stabilization and uptake in Cd and Pb-contaminated soils have received limited attention. This study used biochar (BC) at levels ranging from 0 to 40 t ha-1 as soil amendments in Cd and Pb contaminated rice paddy soil. Biochar significantly decreased soil bioavailable Cd and Pb concentrations 6.7 to 16.6% and 10.6 to 39.7%, respectively, compared to the control. The shoot and root Cd concentrations in Arabidopsis helleri increased significantly by 33.5% and 133.1%, respectively, in the C3 treatment compared to the control. Similarly, shoot Pb concentrations showed a 57.5% increase compared to the control, but no significant changes were observed in root Pb concentrations. The Arabidopsis helleri bioconcentration factor (BCF) saw an increase of up to 40.5% for Cd and 57.8% for Pb with the C3 treatment. Conversely, the Cd translocation factor (TF) decreased 42.8 to 49.1%, while the Pb TF increased 32.8 to 96.6% with biochar application. The majority of Arabidopsis helleri-biochar Cd and Pb was found in the B3 fraction (organic fraction), constituting over 50%, and even over 80% for Cd. The Arabidopsis helleri-biochar primarily contained organic char binding Cd and exhibited slow-release characteristics.